Rotational atherectomy system with stationary cutting elements

ABSTRACT

An elongate tubular body extends between a rotatable cutter and a control. The cutter is connected to the control with a rotatable element. A vacuum is applied through an annular passage defined between the tubular body and the rotatable element. The cutter has at least one radial projection which cooperates with at least one stationary element on the tubular body to cut material drawn into the tubular body. Material that has been processed by the cutter is aspirated through the tubular body for disposal.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/398,241, filed Sep. 17, 1999, which is acontinuation-in-part of U.S. patent application Ser. No. 09/260,199,filed on Mar. 1, 1999, which is a continuation-in-part of U.S. patentapplication Ser. No. 09/058,513, filed on Apr. 10, 1998, now U.S. Pat.No. 6,001,112.

BACKGROUND OF THE INVENTION

[0002] The present invention generally relates to medical devices and,more particularly, to atherectomy catheter devices.

[0003] A variety of techniques and instruments have been developed toremove obstructive material in arteries or other body passageways or torepair the arteries or body passageways. A frequent objective of suchtechniques and instruments is the removal of atherosclerotic plaques ina patient's arteries. The buildup of fatty deposits (atheromas) in theintimal layer (under the endothelium of a patient's blood vessels)characterizes atherosclerosis. Over time, what is initially deposited asrelatively soft, cholesterol-rich atheromatous material often hardensinto a calcified atherosclerotic plaque. The atheromas may be referredto as stenotic lesions or stenoses while the blocking material may bereferred to as stenotic material. If left untreated, such stenoses canso sufficiently reduce perfusion that angina, hypertension, myocardialinfarction, strokes and the like may result.

[0004] Several kinds of atherectomy devices have been developed forattempting to remove some or all of such stenotic material. In one typeof device, such as that shown in U.S. Pat. No. 5,092,873 (Simpson), acylindrical housing, carried at the distal end of a catheter, has aportion of its side-wall cut out to form a window into which theatherosclerotic plaque can protrude when the device is positioned nextto the plaque. An atherectomy blade, disposed within the housing, isthen advanced the length of the housing to lance the portion of theatherosclerotic plaque that extends into the housing cavity. While suchdevices provide for directional control in selection of tissue to beexcised, the length of the portion excised at each pass of theatherectomy blade is necessarily limited to the length of the cavity inthe device. The length and relative rigidity of the housing limits themaneuverability and therefore also limits the utility of the device innarrow and tortuous arteries such as coronary arteries. Such devices arealso generally limited to lateral cutting relative to the longitudinalaxis of the device.

[0005] Another approach, which solves some of the problems relating toremoval of atherosclerotic plaque in narrow and tortuous passageways,involves the use of an abrading device carried at the distal end of aflexible drive shaft. Examples of such devices are illustrated in U.S.Pat. No. 4,990,134 (Auth) and U.S. Pat. No. 5,314,438 (Shturman). In theAuth device, abrasive material such as diamond grit (diamond particlesor dust) is deposited on a rotating burr carried at the distal end of aflexible drive shaft. In the Shturman device, a thin layer of abrasiveparticles is bonded directly to the wire turns of an enlarged diametersegment of the drive shaft. The abrading device in such systems isrotated at speeds up to 200,000 rpm or more, which, depending on thediameter of the abrading device utilized, can provide surface speeds ofthe abrasive particles in the range of 40 ft/sec. According to Auth, atsurface speeds below 40 ft/sec his abrasive burr will remove hardenedatherosclerotic materials but will not damage normal elastic soft tissueof the vessel wall. See, e.g., U.S. Pat. No. 4,990,134 at col. 3, lines20-23.

[0006] However, not all atherosclerotic plaques are hardened, calcifiedatherosclerotic plaques. Moreover, the mechanical properties of softplaques are very often quite close to the mechanical properties of thesoft tissue of the vessel wall. Thus, one cannot always rely entirely onthe differential cutting properties of such abrasives to removeatherosclerotic material from an arterial wall, particularly where oneis attempting to remove all or almost all of the atheroscleroticmaterial.

[0007] Moreover, a majority of atherosclerotic lesions are asymmetrical(i.e., the atherosclerotic plaque is thicker on one side of the arterythan on the other). As will be understood, the stenotic material will beentirely removed on the thinner side of an eccentric lesion before itwill be removed on the thicker side of the lesion. Accordingly, duringremoval of the remaining thicker portion of the atherosclerotic plaque,the abrasive burr of the Auth device or the abrasive-coated enlargeddiameter segment of the drive shaft of the Shturman device willnecessarily engage healthy tissue on the side that has been cleared.Indeed, lateral pressure by such healthy tissue against the abradingdevice is inherently required to keep the abrading device in contactwith the remaining stenotic tissue on the opposite wall of thepassageway. For stenotic lesions that are entirely on one side of anartery (a relatively frequent condition), the healthy tissue across fromthe stenotic lesion will be exposed to and in contact with the abradingdevice for substantially the entire procedure. Moreover, pressure fromthat healthy tissue against the abrading device will be, in fact, theonly pressure urging the abrading device against the atheroscleroticplaque. Under these conditions, a certain amount of damage to thehealthy tissue is almost unavoidable, even though undesirable, and thereis a clear risk of perforation or proliferative healing response. Insome cases, the “healthy tissue” across from a stenotic lesion may besomewhat hardened by the interaction (i.e., it has diminishedelasticity); under such circumstances, the differential cuttingphenomenon described by Auth will also be diminished, resulting in arisk that this “healthy” tissue may also be removed, potentially causingperforation.

[0008] Thus, notwithstanding the foregoing and other efforts to design arotational atherectomy device, there remains a need for such a devicethat can advance through soft atheromas while providing minimal risk ofdislodging emboli, and risk of injury to the surrounding vessel wall.

SUMMARY OF THE INVENTION

[0009] There is provided in accordance with one aspect of the presentinvention, a rotational medical device. The device comprises an elongateflexible tubular body, having a proximal end and a distal end. Arotatable element extends through the body. A rotatable tip at thedistal end of the body is connected to the rotatable element. A controlis provided on the proximal end of the body. At least one radiallyinwardly extending stationary cutting member is provided on the tubularbody, and at least one radially outwardly extending flange on therotatable tip is provided for cooperating with the stationary cuttingmember to cut material drawn into the tubular body.

[0010] In one embodiment, the device comprises two radially outwardlyextending flanges on the tip. The device may also comprise twostationary cutting member on the tubular body. The device may furthercomprise an annular recess in the tubular body, for rotatably receivingthe radially outwardly extending flange. The distal end of the rotatabletip may be either approximately aligned axially with the distal end ofthe tubular body, extend beyond the distal end of the tubular body, orbe recessed within the tubular body.

[0011] In accordance with another aspect of the present invention, thereis provided a method of removing material from a vessel. The methodcomprises the steps of providing an elongate flexible tubular body,having a proximal end and a distal end, a rotatable tip at the distalend of the tubular body, and at least on stationary cutting member onthe tubular body which cooperates with at least one flange on therotatable tip. The distal end of the tubular body is advancedtransluminally to the material, and the rotatable tip is rotated.Portions of the material are drawn proximally past the rotatable tip sothat the material is cut by the action of the flange rotating past thestationary member.

[0012] Preferably, the drawing step is accomplished by applying vacuumto the proximal end of the tubular body. The advancing step generallycomprises advancing the tubular body along a guidewire. Preferably, theadvancing step additionally comprises advancing the tubular body througha percutaneous access site.

[0013] In one aspect of the invention, the method further comprises thestep of infusing fluid through a flush port on the proximal end of thetubular body. The advancing step is accomplished by applying axialdistal pressure on the tubular body, and may include the step ofreducing the amount of axial distal pressure in response to feedbackindicating a change in load on the rotatable tip.

[0014] In accordance with a further aspect of the present invention,there is provided a method of removing material from a patient. Themethod comprises the steps of providing an elongate flexible tubularbody, having a proximal end, a distal end, and at least two radiallyinwardly extending stationary cutting members near the distal end. Arotatable distal tip is carried by the distal end of the tubular body,the tip having at least two radially outwardly extending flanges, and acontrol on the proximal end of the tubular body. The distal tip of thetubular body is advanced to the material to be removed, and the controlis manipulated to activate a vacuum through the tubular body. Rotationof the rotatable tip is commenced to remove material from the patient,and material is sheared between the flanges and the stationary cuttingmembers.

[0015] Further features and advantages of the present invention willbecome apparent to those of skill in the art in view of the disclosureherein, when considered together with the attached drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a schematic view of a device embodying the presentinvention;

[0017]FIG. 2 is a partially sectioned side view of a distal end of thedevice of FIG. 1, showing an embodiment of the cutter assembly;

[0018]FIG. 3 is a side view of the cutter of FIG. 2;

[0019]FIG. 4 is an end view of the cutter of FIG. 3 taken along the line4-4;

[0020]FIG. 5A is a partially sectioned side view of another embodimentof the cutter and housing;

[0021]FIG. 5B is a cross-sectional view of the cutter and housing ofFIG. 5A taken along the lines 5B-5B;

[0022]FIG. 6 is a partially sectioned side view of yet another cutterand housing;

[0023]FIG. 7 is a partially sectioned side view of a further cutter andhousing;

[0024]FIG. 8A is a top perspective view of a serrated cutter configuredin accordance with certain features, aspects and advantages of thepresent invention;

[0025]FIG. 8B is a side view of the serrated cutter of FIG. 8A;

[0026]FIG. 8C is a top view of the serrated cutter of FIG. 8A;

[0027]FIG. 9 is a sectioned side view of a control having features,aspects and advantages in accordance with the present invention;

[0028]FIG. 10A is a schematic illustration of a pinch-valve switch in aposition which interrupts an applied vacuum and interrupts power flow toa drive motor;

[0029]FIG. 10B is a schematic illustration of a pinch-valve switch in aposition that applies the vacuum and interrupts power flow to the drivemotor;

[0030]FIG. 10C is a schematic illustration of a pinch-valve switch in aposition which applies the vacuum and allows power to flow to the drivemotor;

[0031]FIG. 11 is a schematic illustration of a representative motorcontrol circuit in accordance with the present invention;

[0032]FIG. 12 is an enlarged partially sectioned side view of a cutter,housing and catheter assembly configured in accordance with certainaspects and advantages of the present invention;

[0033]FIG. 13 is a schematic view of a treatment process performedaccording to a first mode of off-set operation; and

[0034]FIG. 14 is a schematic view of a treatment process performedaccording to a second mode of off-set operation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0035] With reference initially to FIG. 1, a surgical instrument,indicated generally by reference numeral 10 having features, aspects andadvantages in accordance with the present invention is depicted therein.In general, the illustrative surgical instrument comprises an elongateflexible tubular body 12 having a proximal end 14 and a distal end 16. Acontrol 18 is preferably provided at or near the proximal end 14 of thetubular body 12 for permitting manipulation of the instrument 10. Thecontrol 18 advantageously carries electronic controls and indicators aswell as vacuum controls as will be discussed below.

[0036] With reference now to the partially sectioned view of FIG. 2, thetubular body 12 preferably has an elongate central lumen 20. Desirably,the tubular body 12 has a cutter housing 21 for receiving a cutter 22that may rotate therein. The illustrated cutter 22 is coupled to thecontrol 18 for rotation by way of an elongate flexible drive shaft 24,as will be described below. In an over-the-wire embodiment, the driveshaft 24 may also be provided with an axially extending central lumen 26for slidably receiving a guidewire 28 as will be understood by those ofskill in the art. Moreover, in such configurations, the cutter 22 mayalso have a central lumen.

[0037] The diameter of the guidewire 28 is preferably in the range ofabout 0.010 inch to about 0.020 inch. The lengths of the guidewire 28and the tubular body 12 may be varied to correspond to a distancebetween a percutaneous access site and a lesion being treated. Forexample, the guidewire 28 and the tubular body 12 should be long enoughto allow the cutter 22 of the present surgical instrument 10 to trackalong the guidewire 28 and reach a target occlusion while also allowinga proximal portion of the guidewire 28 to remain exterior to the patientfor manipulation by the clinician (not shown). In an application forremoving coronary artery atheroma by way of a femoral artery access,guidewires having lengths from about 120 cm to about 160 cm may be used,and the length of the tubular body 12 may range between about 50 cm andabout 150 cm, as will be understood by those of skill in art. For otherapplications, such as peripheral vascular procedures includingrecanalization of implanted vascular grafts, the length of the guidewire28 and the tubular body 12 may depend upon the location of the graft orother treatment site relative to the percutaneous or surgical accesssite. Suitable guidewires for coronary artery applications include thosemanufactured by Guidant or Cordis.

[0038] With reference now to FIGS. 3 and 4, the illustrated cutter 22includes a generally cylindrical sleeve shaped body 30 having a centrallumen 32 (FIG. 4). The cylindrical body 30 of the cutter 22 generallyhas an external diameter of between about 0.035 and 0.092 inch. In oneembodiment, the external diameter is approximately 0.042 inch. The body30 has a wall thickness between about 0.003 inch and about 0.010 inch.In one embodiment, the wall thickness is about 0.009 inch. The length ofone embodiment of the present cutter 22 from proximal end 34 to distalend 36 is approximately 0.096 inch but the length may vary from about0.040 inch to about 0.120 inch or more, depending upon the intended use.In general, tip lengths of no more than about 0.100 inch are preferred;shorter tip lengths permit greater lateral flexibility and enableincreased remote access as will be apparent to those of skill in theart.

[0039] With continued reference to FIG. 3, an end cap 38 may be formedon the distal end 36 of the present cutter tip 22. Specifically, thecylindrical body 30 may be machined to create an integral (i.e., onepiece) end cap 38. The end cap 38 may have a thickness of approximately0.007 inch; however, the end cap thickness may range from about 0.003inch to about 0.020 inch. Additionally, it is contemplated that adiscrete end cap 38 may also be separately machined and attached. Forinstance, the end cap 38 may be formed from a more lubricious materialto reduce frictional contact between the guidewire 28 and the end cap38. Such an end cap may be attached in any suitable manner. The end cap38 preferably has an outside diameter that substantially corresponds tothe outside diameter of the distal end 26 of the present cutter tip 22.The end cap outside diameter may, however, substantially correspond tothe inside diameter of the cylindrical body in some embodiments.

[0040] The end cap 38 may also have a centrally located aperture 39. Theaperture 39, if present, preferably has a diameter of between about0.013 inch and about 0.025 inch. In one embodiment, the aperture 39 hasa diameter of approximately 0.022 inch. Desirably, the aperture 39 mayaccommodate a guidewire 28 or allow fluids to flow therethrough. As willbe appreciated, the cutter 22 may have a machined or otherwiseintegrally formed radially inwardly extending annular flange 41 (seeFIG. 6). It is also anticipated that aspects of the present inventionmay also be practiced without employing an end cap or inwardly extendingannular flange 41. In such configurations, the flange 41 may extendfully around the circumference of the cutter 22 or may have portionsremoved such that the annular flange 41 is actually a series of inwardlyprojecting tabs. Additionally, an outside distal edge of the end cap 38or annular flange 41 is desirably broken, chamfered or rounded such thatany sharp edge resulting from manufacturing may be removed, and suchthat the end cap may be rendered substantially atraumatic.

[0041] With reference now to FIGS. 2-4, a connector portion 40 ispreferably provided at or near the proximal end 34 of the illustratedcutter 22 for securing the cutter 22 within the cutter housing 21 suchthat the cutter may rotate therein. Additionally, the connector portion40 may be a mechanical, self-locking method to secure the rotatingcutter 22 within the cutter housing 21 and to guard against undesiredaxial movement of the cutter 22 relative to the housing 21. In certainembodiments, axial movement of the cutter may be accommodated within thehousing 21, and even within the tubular body 12, as will be discussedbelow in more detail.

[0042] As will be recognized by those of skill in the art, safetystraps, redundant glue joints, crimping, and swaging are commonly usedto create redundant failure protection for catheter cutter tips. Theadvantageous structure of the present connector portion 40 retains thecutter tip 22 within the cutter housing 21 and may reduce the need forsuch multiple redundancies. As will be described, the connector portion40 may take various forms.

[0043] In embodiments similar to the one illustrated in FIGS. 2-4, theconnector portion 40 generally comprises two outwardly extending radialsupports, such as a set of wedge-shaped flanges 42. The flanges 42 maybe formed by removing material from an annular circumferential flange atthe proximal end 34 of the cutter 22. The flanges 42 may be formed intothe illustrated wedge-shape, although other shapes may also bedesirable. The flanges 42 may also be bent from a proximal extension ofthe wall of tubular body 30, or adhered or otherwise secured to theproximal end 34 of the cutter 22. Moreover, as will be recognized by oneof ordinary skill in the art, the cutter 22 and flanges 42 may be castor molded using any suitable method dependent upon the material chosen.As will be recognized by those of ordinary skill in the art, the flanges42 may alternatively be connected to tubular body 30 at a point inbetween the proximal end 34 and the distal end 36 of the cutter tip.

[0044] Although two opposing flanges 42 are illustrated in FIGS. 2-4,three or more flanges 42 may be utilized, as will be apparent to thoseof skill in the art. In general, the flanges 42 should be evenlydistributed around the circumference of the cutter 22 to improve balanceduring rotation of the cutter 22. For example, three flanges 42 wouldpreferably extend radially outward from the cylindrical wall of the body30 on approximately 120° centers. Similarly, four outwardly extendingradial flanges 42 would preferably be located on approximately 90°centers.

[0045] With reference now to FIGS. 8A-8C, another configuration of theconnector portion 40 is illustrated therein. In the illustratedconfiguration, the outwardly extending radial supports 42 are alsoformed by removing material from an annular circumferential flange atthe proximal end of the cutter 22. The supports 42 are attached to thebalance of the cutter 22 with tangs 43 that are carved from the cutter22 when the supports 42 are formed. In this manner, the tangs 43 do notrequire the slots that form the arms described above. Of course, acombination of the slots and arms and the tangs without slots may alsobe used to attach the flange 42 to the cutter 22. In the illustratedembodiment, the tangs 43 preferably are between about 0.010 inch andabout 0.050 inch in length. More preferably, the tangs 43 are about0.015 inch long. In one embodiment, the tangs are about 0.25 inch long.The tangs also have a width between about 0.010 inch and about 0.050inch. In a presently preferred embodiment, the tangs have a width ofabout 0.020 inch.

[0046] The illustrated connector portion 40 has an outside diametertaken about the opposing flanges 42 of approximately 0.071 inch.Generally, the outside diameter may range from about 0.057 inch to about0.096 inch in a device intended for coronary artery applications. Thethickness of the flanges 42 in the axial direction (i.e., the dimensionnormal to the increase in diameter resulting from the flanges) is about0.010 inch but may range from about 0.004 inch to about 0.025 inch. Ingeneral, an outside diameter defined about the flanges 42 may beselected to cooperate with the inside diameter of an annular retainingrace or groove 54 in the housing 21, discussed below, to axially retainthe cutter 22 while permitting rotation of the cutter 22 relative to thehousing 21. The thickness of the flanges 42 and the axial width of theretaining groove 54 also are generally designed to either allow axialmovement of the cutter 22 within the housing 21 or to limit or eliminatesubstantial axial movement of the cutter 22 within the housing 21, as isdiscussed below.

[0047] With continued reference to now FIG. 3, each illustrated flange42 is preferably attached to the cutter 22 by a spring arm 43. Each arm43 is defined by two longitudinally extending slots 44 which are formedin the cylindrical wall of the body 30 adjacent each flange 42. Theslots 44 are preferably about 0.005 inch in width; however the width mayrange from approximately 0.001 inch to approximately 0.025 inch. Theslots 44 of the present cutter 22 are also generally at least about0.025 inch in axial length along the longitudinal axis of the body 30.One skilled in the art will readily appreciate that the slots 44 of thepresent cutter 22 can be varied in axial length to vary the length ofthe cantilevered arm 43 that connects the flanges 42 to the cutter 22.The slots 44, and the arm 43 defined between the slots 44, and thetangs, allow radial inward compression of the flanges 42 and spring arms43, or tangs, to ease assembly of the cutter 22 within the cutterhousing 21 as described below.

[0048] Desirably, the cutter 22, and especially the portion containingthe slots 44, is made of a material having an adequate spring constantas will be understood by those of skill in the art. In one embodiment,the cutter 22 is made from a medical grade stainless steel alloy. Thechosen material preferably has characteristics including the ability toallow the cantilevered spring arm 43 to deflect radially inwardly anadequate distance over the length of the arm 43 without exceeding theelastic limit of the material (i.e., the deflection is an elasticdeformation). As is known, elastic deformations allow structures todeflect and substantially return to their initial shape or position. Forinstance, special hardening methods may be used to maintain theelasticity of the selected material in the deflection range necessaryfor a specific application.

[0049] With reference now to FIG. 2, the cutter 22 is snap fit into thecutter housing 21. Advantageously, the arms 43 may be deflected radiallyinward such that the cutter 22 may be inserted into the cutter housing21 through an aperture or lumen having a smaller ID than the insidediameter of the retaining groove 54 of the cutter housing 21.Preferably, the cutter 22 is inserted from the distal end of the housing21 and slid proximally through the housing 21 until the flanges 42 snapoutward into the race 54. Thus, the cutter 22 will be retained in thishousing even if it separates from its drive element 24. Desirably, thearms 43 substantially return to their original, relaxed positions withinthe retaining groove 54 the cutter housing 21 following installation. Itshould be appreciated that the arms 43 may also be maintained under aslight bending stress (i.e., the inside diameter of the race 54 may besmaller than the outside diameter about the relaxed flanges 42) ifdesired.

[0050] With reference now to FIGS. 2-7, an external element for cuttingor manipulating occlusions, such as thrombus, will be described indetail. The element may include a thread 46 that extends along a portionof the exterior surface of the body 30 of the present cutter 22. Thethread 46 preferably extends distally from a location on the body 30that is distal to the connector 40. The thread 46 may be manufacturedusing any suitable technique well known to those of skill in the art.

[0051] In one embodiment having a cutter housing 21 with an insidediameter of about 0.0685 inch, the major diameter of the thread 46 isapproximately 0.0681 inch. However, the major diameter of the presentthread 46 may range from about 0.050 inch to about 0.130 inch orotherwise, depending upon both the inner diameter of the cutter housingand the intended clinical application. The thread 46 of the foregoingembodiment has a pitch of approximately 0.0304 inch and is desirablyhelical. The pitch may range from about 0.005 inch to about 0.060 inch,and may be constant or variable along the axial length of the cutter 22.The thickness of the present thread 46 in the axial direction isapproximately 0.008 inch; however, the thickness may range from about0.003 to about 0.05, and may be constant or variable along the length ofthe thread 46. Thus, it is anticipated that the cutters 22 may also havea generally spiral helix thread.

[0052] In some of the illustrated embodiments, the thread 46 extendsapproximately two complete revolutions around the cylindrical body 30.The thread 46 may be a continuous radially outwardly extending ridge asillustrated, or may comprise a plurality of radially outstanding bladesor projections preferably arranged in a helical pattern. The thread 46may extend as little as about one-half to one full revolution around thecutter body 30, or may extend as many as 2½ or 3 or more fullrevolutions around the circumference of the body 30, as is discussedmore below. Optimization of the length of the thread 46 may beaccomplished through routine experimentation in view of the desiredclinical objectives, including the desired maneuverability (i.e.,tractability through tortuous anatomy) and the length of the cutter 22,as well as the nature of the cutting and/or aspiration action to beaccomplished or facilitated by the cutter 22. In addition, while thepresent cutter 22 is illustrated and described as having a singlethread, one skilled in the art will appreciate that the cutter 22 mayalso have multiple threads, a discontinuous thread or no threads.

[0053] Referring now to FIGS. 6 and 7, the thread 46 illustrated thereinis a constant pitch and varies in cross-section along its length from arelatively low profile at the distal end 36 to a relatively higherprofile at the proximal end 34 of the cutter tip 22. Such a rampedthread 46 improves performance when the catheter encounters more denseobstructive material. In such an embodiment, the major diameter of thedistal lead 47 of the thread 46 is smaller than the major diameter ofthe thread along the more proximal portions of the cutter shaft 30. Itis anticipated that the pitch of the thread 46 may also vary along withthe profile of the thread 46 to alter the clinical effects accomplished.

[0054] As discussed directly above, the pitch of the thread 46 may alsobe varied along the axial length of the cutter body 30. Varying thepitch allows a modified function at different points along the axiallength of the cutter 22, such as a greater axial thread spacing at thedistal end 36 of the cutter 22 to engage material and a relativelycloser axial spacing of the threads at the proximal end 34 of the cutter22 for processing the material. In general, the pitch may range fromabout 0.010 inch at the distal end to about 0.080 inch at the proximalend. In one embodiment, the pitch at the distal end 36 is approximately0.034, the pitch at the proximal end 34 is approximately 0.054, and thepitch varies continuously therebetween. The maximum and minimum pitch,together with the rate of change of the pitch between the proximal end34 and the distal end 36 can be optimized through routineexperimentation by those of skill in the art in view of the disclosureherein.

[0055] With reference to FIG. 6, the ramped thread diameter results in adistal portion 36 of the cutter 22 that can extend distally beyond thecutter housing 21 and a proximal portion 34 of the cutter tip 22 thatwill be retained within the cutter housing 21. This results, in part,from a radially inwardly extending retaining flange 41 which reduces thediameter of the opening 39 at a distal end 52 of the cutter housing 21relative to an internal bore of the housing 21. As shown in FIG. 3, thedistal portion 45 of the thread 46 may have its leading edge broken,chamfered or rounded to remove a sharp corner or edge. By eliminatingthe sharp corner or edge, the risk of accidental damage to the patientis reduced. The distal edge of the cylindrical body 30 and the flanges42 may also be broken, chamfered or otherwise rounded to eliminate orreduce sharp edges.

[0056] With reference to FIG. 2, the outside diameter of the thread 46in this embodiment has a close sliding fit with the inside diameter, orinner wall, of the cutter housing 21. In this configuration, theatheromatous material will be avulsed by the threads 46, fed furtherinto the housing 21 toward the flanges 42 and chopped or minced by theflanges 42. To further enhance the chopping or mincing action of theflanges 42, a stationary member (not shown) or a set of stationarymembers (not shown) may be positioned such that the rotating flanges 42and the stationary member or members (not shown) effect a shearingaction. The shearing action breaks up the strands into shorter sections,which are less likely to clog the instrument, as described below.Moreover, the flanges 42 may be provided with sharply chamfered leadingor trailing edges to alter their cutting action, if desired.

[0057] It may be desirable in some embodiments to provide an annularspace between the outside diameter of the thread 46 and the insidediameter of the cutter housing 21. By spacing the thread 46 apart fromthe inside wall of the central lumen 20, an annular space is providedfor material to pass through the cutter housing 21 without being severedby the thread 46 of the cutter tip 22. This may be utilized inconjunction with vacuum, discussed below, to aspirate material into theatherectomy device without the necessity of complete cutting by thethread 46 or flanges 42. This may be advantageous if the rate ofmaterial removal effected by aspiration is higher than the rate at whichmaterial removal may occur with the thread 46 engaging such material. Inaddition, the rotational atherectomy device 10 may more readily aspiratecertain lesion morphologies, such as those including portions ofcalcified plaque, if the thread 46 is not required to cut all the waythrough the aspirated material. In general, the desired radial distancebetween the thread 46 and the inside wall of the cutter housing 21 willbe between about 0.0001 inch and about 0.008 inch, to be optimized inview of the desired performance characteristics of the particularembodiment. In an embodiment intended solely to aspirate soft atheromas,the cutting function of the thread 46, or the thread 46 itself, may bedeleted entirely, so that cutting occurs by the flanges or cuttingblocks 42 and/or stationary members (not shown) in cooperation with theaspiration provided by a vacuum source.

[0058] Interventions for which an atraumatic distal tip is desired, suchas, for example but without limitation, saphenous vein graphs, can bewell served by an atraumatically tipped cutter 22, as illustrated inFIG. 7. The blunt tip cutter 22 preferably has a bulbous or rounded tip23 that extends from the distal end of the cutter 22. The tip 23preferably has a radially symmetrical configuration such that uponrotation it presents a smooth, atraumatic surface for tissue contact.Viewed in side elevation, such as in FIG. 7, the tip 23 may have agenerally hemispherical, oval, elliptical, aspheric or other smoothcurve on its radial surface with either a curved or truncated (i.e.,flat) distal surface. As will be recognized, the shape of the tip 23 maybe varied to achieve desirable effects on the catheter crossing profileor on soft atheromas, etc. In general, the tip 23 advantageouslyminimizes the possibility of traumatic contact between the healthy wallof the vessel and the thread 46 or other cutting element.

[0059] The outside diameter of the tip 23 may range from the outsidediameter of the cutter body 30 to the outside diameter of the cutterhousing 21. Diameters greater than the housing 21 may also be used, butdiameters smaller than the housing 21 facilitate a smaller crossingprofile of the instrument 10. The axial length of the tip 23 may bevaried to suit the intended application, but will generally be withinthe range of from about 0.050 inch to about 0.100 inch in a coronaryartery application.

[0060] The outside surface of tip 23 may be provided with surfacetexturing or treatments. As will be recognized by those of skill in theart, the surface texturing or treatments may be formed by abrasivecoating (i.e., coating the tip with diamond particles), acid etching orany other suitable method. The texture or treatments may be on thedistal surface or the lateral surfaces or both such that a two-stageinteraction with the encountered materials may occur. Thus, the tip canbe used for grinding or otherwise remodeling the encountered materials.For example, an abrasive distal surface can be used to cut throughcalcified plaque, while a smooth radial surface can compress softmaterial against the vessel wall to facilitate acceptance into thehelical thread 46 of the cutter 22. Varying the distance between thedistal end 47 of the thread 46 and the proximal end of the tip 23, aswell as varying its geometry, can allow adjustments to the cutteraggressiveness. For instance, the thread 46 may extend up to theproximal edge of the tip 23 and allow early engagement of theencountered materials relative to a cutter 22 having a length ofunthreaded shaft between the proximal edge of the tip 23 and the distalend 47 of the thread 46.

[0061] The tip 23 can be integrally formed with the cutter tip 22, suchas by machining techniques known in the art. Alternatively, it can beseparately formed and secured thereto, such as by soldering, adhesives,mechanical interference fit, threaded engagement and the like. The tipcan be machined from a suitable metal or molded or otherwise formed froma suitable polymeric material such as polyethylene, nylon, PTFE orothers known to those of ordinary skill in the art.

[0062] Moreover, the cutter tip 22 itself may be machined such that thedistal facing end is serrated or discontinuously formed. Thediscontinuous thread may comprise a number of inclined surfaces formingdistally facing teeth. In such cutters, the cutter is more aggressive inthe forward direction. With reference to FIGS. 8A-8C, such a cutter tip22 may have serrations 57 formed along the distal end 47 of the thread46. The serrations may also be positioned on an extended nose portion(not shown) of the cutter. The serrations 57 preferably are formed toextend outward radially from the center axis of the cutter 22. While theillustrated serrations 57 are formed in a straight line, the serrations57 may also be arcuate in shape to form a sickle-shaped cutting surface.The illustrated serrations 57 preferably have a depth of between about0.0005 inch and about 0.0040. More preferably, the serrations 57 areabout 0.0020 deep. The serrations 57 also preferably are formed with asloping face 59 that is at an angle 1 of between about 45° and about 85°with a longitudinal plane that extends through the axis of rotation. Ina presently preferred arrangement, the sloping face extends at an angleof about 60° relative to the same plane. Moreover, the run of thesloping face 59 is preferably between about 0.0020 inch and about 0.0050inch. In the preferred arrangement, the run is about 0.0035 inch inlength. The serrations in the illustrated cutter extend over only aforward facing portion 45 of the distal end 36 of the cutter 22;however, it is anticipated that the cutter 22 may also comprise aserrated thread that extends the entire length of the thread 46.

[0063] In many interventions, it is desirable to have the cutter 22floating axially within the housing 21. FIG. 6 illustrates a cutter 22arranged to float axially within the housing 21. Preferably, in suchconfigurations, the cutter 22 is provided with an anti-locking threaddesign. For instance, the thread 46 may be configured such that itcannot jam within the housing 21 at either extreme of axial travel. Sucha configuration may involve having a minimum thread major diameter whichis greater than the diameter of the opening in the distal end of thedevice 10 or having a pitch which is less than the thickness of the ringflange 41 formed at the distal tip of the cutter housing 21. Otherconfigurations may also be readily apparent to those of ordinary skillin the art. The axial travel and the thread design desirably cooperateto allow the cutter 22 to self-adjust to digest soft fibrous material.

[0064] The housing 21 may conveniently be assembled from two pieces, toentrap the cutter 22 therein. The two pieces are then laser-welded orotherwise secured together. In one embodiment, the housing 21 may besplit longitudinally, the cutter 22 inserted, and the two pieces maythen be secured together. In another presently preferred embodiment, thetwo pieces may split the housing 21 into a distal component and aproximal component (see FIG. 6). The two components may be assembled totrap the cutter 22 therein and may then be laser-welded or otherwisesecured together. Such assemblies allow for the cutter 22 to be capturedwithin the cutter housing 21 as well as allow for certain relativelyloose manufacturing tolerances for the cutter 22 and the cutter housing21 such as will reduce manufacturing costs. Such assemblies also enablebetter fits because the flanges 42 require less travel (i.e., theflanges 42 do not require deflection for insertion into the housing 21).

[0065] Desirably the cutter 22 is positively retained in the cutterhousing 21 for rotation, as discussed directly above. With referenceagain to FIG. 2, the illustrated housing 21 internally may be a steppedcylinder having a proximal end 50 and the distal end 52. In someembodiments featuring axial movement of the cutter 22 relative to thecutter housing 21 or tubular body 12, an annular bearing surface 48 (seeFIG. 6) provides a proximal limit of travel for the flanges 42 on cutter22. Notably, the annular bearing surface 48 may be formed within thecutter housing 22 (as illustrated in FIG. 6) or within the tubular body12 (not shown).

[0066] In a specific coronary artery embodiment, the internal diameterof the distal portion 52 of the cutter housing 21 is approximately0.0689 inch and may range from about 0.050 inch to about 0.150 inch. Theproximal end 50 of the present cutter housing 21 preferably has aninternal diameter of approximately 0.0558 inch. The internal diameter 50of the proximal end of the present cutter housing 21 may range fromabout 0.035 inch to about 0.130 inch. At its distal end 52, the cutterhousing 21 may be provided with a radially inwardly extending retaininglip, such as flange 41 in FIG. 6, sized and configured such that thecutter 22 is captured within the cutter housing 21 and such that thecutter 22 cannot screw itself out of its captured position within thecutter housing 21.

[0067] The exterior diameter of the distal end 52 of the cutter housing21 in one embodiment is approximately 0.0790 inch; however, the distalexterior diameter may range from about 0.039 inch to about 0.150 inchdepending upon cutter design and the intended clinical application. Thedistal portion 52 of the cutter housing 21 in the illustrated embodimentis about 0.117 inch in length but the length may vary from about 0.020inch to about 0.50 inch. In the embodiment illustrated in FIG. 2, theoutside diameter of the proximal portion 50 of the cutter housing 21 maybe less than the diameter of the distal portion 52 to produce an annularshoulder 51 to limit concentric proximal advance of the proximal sectionwithin the tubular body 12. The proximal section of the housing 50extends axially for approximately 0.09 inch but its length may vary aswill be understood by those of skill in the art.

[0068] In general, the cutter housing 21 may be integrally formed orseparately formed and secured to the distal end 16 of the tubular body12 in accordance with any of a variety of techniques which will be knownto those of skill in the art. The concentric overlapping jointillustrated in FIG. 2 can be utilized with any of a variety of secondaryretention techniques, such as soldering, the use of adhesives, solventbonding, crimping, swaging or thermal bonding. Alternatively, or inconjunction with any of the foregoing, an outer tubular sleeve (notshown) may be heat shrunk over the joint between the cutter housing 21and the tubular body 12. While not shown, it is presently preferred toslide the proximal end 50 of the cutter housing 21 over the distal end16 of the tubular body 12 and apply a fillet of adhesive about theproximal extremity of the cutter housing 21 to hold the two componentstogether. In such a configuration, the proximal portion 50 of the cutterhousing 21 desirably does not block a portion of the annual recessdefined between the central lumen 20 and the outer surface of the driveelement 24. It is anticipated that this style of connection can beutilized with any of the cutter housing features described herein andthat the cutter housing 21 may be provided with an internal stop tolimit axial displacement of the cutter housing 21 relative to the distalend 16 of the tubular body 12.

[0069] With reference again to FIG. 2, at the proximal interior end ofthe distal component 52 of the housing 21 is the shallow outwardlyextending annular retaining race or groove 54 introduced above. Theretaining race 54 in one embodiment is approximately 0.0015 inch deeprelative to the inner diameter of the distal section 52 and may range indepth from about 0.0005 inch to about 0.020 inch. The retaining race 54in the illustrated embodiment is about 0.0135 inch in axial width;however, as one skilled in the art will readily appreciate, the racewidth may be varied and still accomplish its retention function as isdiscussed further below. Moreover, the race 54 may be locatedproximally, or extend proximally, of the cutter housing 21 such that thecutter 22 may be retracted within the tubular body 12.

[0070] The retaining race 54 cooperates with the flanges 42 of thepresent cutter 22 to retain the cutter 22 within the cutter housing 21as described in detail above. The flanges 42 provide a bearing surfacefor the cutter 22 to facilitate rotational movement of the cutter 22relative to the housing 21. In addition, where the axial dimensions ofthe flanges 42 and the race 54 are approximately the same, the cutter 22may be substantially restrained from axial movement within the cutterhousing 21. As will be appreciated, the race 54 may be larger in axialwidth relative to the thickness of the flanges 42 to allow axialmovement of the cutter 22 within the cutter housing 21 or even into thetubular body 12 as discussed above.

[0071] With continued reference to FIG. 2, the distal extremity of theillustrated cutter 22 may be approximately aligned with the distalextremity of the cutter housing 21. As such, the length of the cutterhousing 21 distal of the retaining groove 54 substantially correspondsto the length of the portion of the of the cutter 22 which extendsdistally of the distal surfaces of flanges 42. By creating asubstantially flush positioning at the distal end 52 of the cutterhousing 21 and the cutter 22, the possibility of accidental damage tothe intima by the cutter 22 is reduced. One skilled in the art willreadily recognize, however, that the distal end 36 of the cutter 22 mayalternatively extend beyond, or be recessed within, the distal end 52 ofthe cutter housing 21 (i.e., the embodiment of FIG. 7). Additionally,the cutter 22 may be arranged for selective extension and retractionrelative to the cutter housing 21, the benefits of which are describedbelow.

[0072] Another cutter 60 and associated cutter housing 70 areillustrated in FIGS. 5A and 5B. Although the cutter 60 embodies many ofthe same features as the cutter 22 described above, like elements willgenerally be called out by new reference numerals for ease ofdiscussion. It should be recognized, however, that any of the features,aspects or advantages of the cutter 22 described above and the cutter 60described below may be easily interchanged by one of ordinary skill inthe art.

[0073] The cutter 60 is preferably symmetrical about the rotational axishaving a body 61 with an annular retention structure, such as aretaining race 62, located near the body's proximal end 64. Theretaining race 62, or connector portion, in the illustrated embodimentis about 0.007 inch deep, and about 0.008 inch wide, although bothdimensions can be varied as may be desired and still achieve the desiredretention function, as will be readily recognized by one with skill inthe art. Proximal to the retaining race 62, the outside diameter of thebody 61 is rounded or tapers from about 0.04 inch to about 0.036 inch.Preferably, all edges are broken, chamfered or otherwise rounded toensure burr free and dull corners and to facilitate assembly. The cutter60 may also have a thread 66 similar to that described above.

[0074] The cutter 60 is preferably snap fit into the cutter housing 70by inserting the cutter 60 into the distal end 74 of the cutter housing70. The cutter housing 70 is preferably similar to that described abovewith the exception that the retaining race 54 of the first housing isreplaced by a set of inwardly extending radial retaining members 72.With reference to FIG. 5B, the present cutter housing 70 has threeretaining members 72, preferably circumferentially symmetricallydistributed (i.e., on about 120∞ centers). One skilled in the art willrecognize that the number, size and shape of the retaining members canvary; at least two will generally be used to achieve opposition, andembodiments having 3, 4, 5 or more may be readily utilized. It ispossible, however, to utilize a single retaining member in someapplications such that the single retaining member operates as astationary cutter member either with or without a set of cutter blocks(42 in the embodiments described above).

[0075] As with the arms 43 above, the retaining members 72 are sized andconfigured to allow deflection within the elastic range such that theretaining members 72 may be deflected and inserted into the race 62 asdiscussed below. Again, this snap fit configuration advantageouslyenables the cutter 60 to be retained in the cutter housing 70 even ifthe cutter 60 separates from the driving element (not illustrated).

[0076] As introduced directly above, the retaining members 72 may servethe added function of stationary cutting members. As such the retainingmembers 72 may be sized accordingly. The illustrated retaining members72 are about 0.007 inch thick in the axial direction; however, oneskilled in the art will appreciate that the thickness can range fromabout 0.003 inch to about 0.030 inch or otherwise depending uponmaterial choice and the desired degree of axial restraint. The retainingmembers 72 extend about 0.007 inch inward from the interior wall of thecylindrical cutter housing 70. The retaining member 72 length can vary,however, depending upon the desired dimensions of the cutter housing 70and the cutter 60. As shown in FIG. 5B, the side edges 73 of theretaining members 72 may be provided with a radius such that the radialinterior and exterior ends are wider than the central portion.Additionally, while shown with a concave radius, the stationaryretaining members 72 may alternatively be provided with a convex radius(not shown) to form a smoothly transitioning profile.

[0077] As one skilled in the art will appreciate, the retaining members72 are provided to engage within the retaining race 62 of the cutter 60.The retaining members 72 and the race 62 may be sized and configuredsuch that the cutter 60 is either substantially restrained from axialmovement relative to the cutter housing 70 or some axial travel isallowed between the two components. The retaining members 72 may alsoprovide a bearing surface for the rotational movement of the cutter 60relative to the cutter housing 70. For instance, the race 62 of thecutter 60 desirably rides on the ends of the retaining members 72 suchthat the retaining members 72 provide bearing surfaces at their innermost edges and allow the cutter 60 to be rotated relative to the housing70. Similar to the assembly described above, the distal end 65 of thecutter 60 may be approximately flush with the distal end 74 of thecutter housing 70. Alternatively, the distal end 65 of the cutter 60 mayextend distally from or may be slightly recessed within the distal end74 of the cutter housing 70 by as much or more than is shown in FIG. 5A.Moreover, in specific applications, the cutter 60 may be selectivelyadvanced or retracted relative to the cutter housing 70, enablingadvantages that are described below.

[0078] With reference again to FIG. 2, the distal end of a flexibledrive shaft 24 may be firmly secured within an axial bore 32 of thecutter 22. The cutter 22 may be secured to the flexible drive shaft 24by any of a variety of ways such as crimping, swaging, soldering,interference fit structures, and/or threaded engagement as will beapparent to those of skill in the art. Alternatively, the flexible driveshaft 24 could extend axially through the cutter 22 and be secured atthe distal end 36 of the cutter 22.

[0079] In any of the embodiments described herein, the cutter 22 and thecutter housing 21 may be designed so that the cutter 22 may bepositioned within the cutter housing 21 in a manner that allows axialmovement of the cutter 22 relative to the cutter housing 21.Controllable axial movement of the cutter 22 may be accomplished in avariety of ways, to achieve various desired clinical objectives. Forexample, in either of the embodiments illustrated in FIGS. 2 and 5a, aminor amount of axial movement can be achieved by increasing the axialdimension of the annular recesses 54, 62 with respect to the axialdimension of the flanges 42, or retaining members 72. The annularproximal stop 48 (FIG. 2) can be effectively moved proximally along thetubular body 12 to a position, for example, within the range of fromabout 5 centimeters from the distal end 52 to at least about 10 or 20centimeters from the distal end 52. This permits increased lateralflexibility in the distal 10 cm or 20 cm or greater section of thetubular body 12. Alternatively, the proximal stop 48 can be eliminatedentirely such that the entire inside diameter of the tubular body 12 isable to accommodate the flanges 42 or their structural equivalent, orthe outside diameter of the thread 46, depending upon the embodiment.Limited axial movement can also be accomplished in the mannerillustrated in FIGS. 6 and 7, as will be appreciated by those of skillin the art.

[0080] In general, relatively minor degrees of axial movement, such ason the order of about one or two millimeters or less may be desirable tohelp reduce the incidence of clogging and also reduce trauma, such as bythe distal cutting tip pressing against a vessel wall. Minor axialmovability can also help compensate for differential elongation orcompression between the tubular body 12 and the drive shaft 24.

[0081] A greater degree of axial movability may be desirable inembodiments in which the cutter 22 may be controllably extendedpartially beyond the housing 21 such as to improve engagement with hardobstructive material. Retraction of the cutter 22 within the cutterhousing 21 may be desirable during insertion of the device 10, tominimize trauma to the vascular intima during positioning of the device10. The cutter 22 may thereafter be advanced distally on the order of 1to 3 or 5 millimeters beyond the distal end 52 of the housing 21, suchas to engage obstructive material to be drawn into the cutter housing21.

[0082] More significant proximal retraction of the cutter 22 within thehousing 21, such as on the order of 5 to 20 centimeters from the distalend 52, may be advantageous during positioning of the atherectomycatheter. As is understood in the art, one of the limitations onpositioning of a transluminal medical device within tortuous vascularanatomy, particularly such as that which might be encountered in theheart and intracranial space, is the lateral flexibility of the distalportion of the device. Even if the outside diameter or crossing profileof the device is small enough to reach the stenotic region, the devicestill must have sufficient pushability and sufficient lateralflexibility to navigate the tortuous anatomy.

[0083] In the context of rotational atherectomy catheters, the rotatabledrive shaft 24, as well as the cutter 22, can significantly increase therigidity of the catheter. In accordance with the present invention, thedrive shaft 24 and the cutter 22 may be proximally withdrawn within thetubular housing 12 to provide a relatively highly flexible distalcatheter section that is capable of tracking a guidewire 28 throughtortuous vascular anatomy. Once the outer tubular housing 12 of theatherectomy catheter has been advanced to the treatment site, the cutter22 and the drive shaft 24 may be distally advanced through the tubularbody 12 and into position at the distal end 16. In this manner, therotational atherectomy catheter can be positioned at anatomicallocations that are not reachable if the drive shaft 28 and housing 21 atthe distal end 16 of the tubular body 12 are advanced as a single unit.

[0084] In general, the cutter 22 is preferably proximally retractablefrom the distal end 52 of the cutter housing 21 by a distance sufficientto permit the outer tubular body 12 and cutter housing 21 to bepositioned at the desired treatment site. In the context of coronaryartery disease, the distance between the distal end 52 of the cutterhousing 21 and the retracted cutter 22 is generally be within the rangeof from about 5 cm to about 30 cm and preferably at least about 10 cm.Proximal retraction of the cutter 22 over distances on that order willnormally be sufficient for most coronary artery applications.

[0085] The flexible drive shaft 24 is preferably a hollow, laminatedflexible “torque tube” such as may be fabricated from an inner thin-wallpolymeric tubing, an intermediate layer of braided or woven wire, and anouter polymeric layer. In one embodiment, the torque tube comprises apolyimide tube having a wall thickness of about 0.004 inch, with a layerof braided 0.0015 inch stainless steel wire embedded therein. Thelaminated construction advantageously produces a tube with a very hightorsional stiffness and sufficient tensile strength, but which isgenerally laterally flexible. However, depending upon the desired torquetransmission, diameter and flexibility, any of a variety of othermaterials and constructions may also be used. In general, the driveshaft 24 should have sufficient torsional rigidity to drive the cutter22 through reasonably foreseeable blockages. It is also recognized thatin some applications, the drive shaft 24 may be a wire or other solidconstruction such that no inner lumen 26 extends therethrough.

[0086] The outside diameter of one embodiment of the present hollowflexible drive shaft 24 is approximately 0.032 inch, but may rangebetween about 0.020 inch and about 0.034 inch or more. One skilled inthe art will appreciate that the diameter of the flexible drive shaft 24may be limited by a minimum torsional strength and a guidewire diameter,if a guidewire 28 is present, at the low end, and maximum permissiblecatheter outside diameter at the high end.

[0087] The selection of a hollow drive shaft 24 allows the device 10 tobe advanced over a conventional spring-tipped guidewire 28, andpreferably still leaves room for saline solution, drugs or contrastmedia to flow through the lumen 26 of the drive shaft 24 and out of thedistal opening 39 on the cutter 22. The internal diameter of the presenthollow flexible drive shaft 24 is thus partially dependent upon thediameter of the guidewire 28 over which the flexible drive shaft 24 musttrack. For example, the internal diameter of the guidewire lumen 26 inone embodiment of the present hollow flexible drive shaft 24, intendedfor use with a 0.018 inch diameter guidewire, is approximately 0.024inch. Because the flexible drive shaft 24 preferably extends between thecontrol 18 and the cutter 22, the length of the present hollow flexibledrive shaft 24 should be sufficient to allow the cutter assembly toreach the target location while also allowing adequate length outside ofthe patient for the clinician to manipulate the instrument 10.

[0088] With reference again to FIG. 2, the lumen 20 of the assembleddevice 10 is thus an annular space defined between the inside wall ofthe flexible tubular body 12 and the outside of the flexible drive shaft24. This lumen 20 may be used to aspirate fluid and material from thecutter. Preferably, sufficient clearance is maintained between thetubular body 12 and the rotating drive shaft 24 to minimize thelikelihood of binding or clogging by material aspirated from thetreatment site.

[0089] In general, the cross-sectional area of the lumen 20 ispreferably maximized as a percentage of the outside diameter of thetubular body 12. This permits an optimization of lumen cross-sectionalarea which maintains a minimal outside diameter for tubular body 12,while at the same time permitting an acceptable flow rate of materialthrough the aspiration lumen 20, with minimal likelihood of clogging orbinding which would interrupt the procedure. Cross-sectional area of theaspiration lumen 20 thus may be optimized if the drive tube 24 isconstructed to have relatively high torque transmission per unit wallthickness such as in the constructions described above. In oneembodiment of the invention, intended for coronary artery applications,the outside diameter of tubular body 12 is about 0.080 inch, the wallthickness of tubular body 12 is about 0.008 inch, and the outsidediameter of the drive shaft 24 is about 0.031 inch. Such a constructionproduces a cross-sectional area of the available aspiration portion ofcentral lumen 20 of about 0.00245 square inch. This is approximately 50%of the total cross-sectional area of the tubular body 12. Preferably,the cross-sectional area of the lumen 20 is at least about 25%, morepreferably at least about 40%, and optimally at least about 60% of thetotal cross-sectional area of the tubular body 12.

[0090] The tubular body 12 may comprise any of a variety ofconstructions, such as a multi-layer torque tube. Alternatively, any ofa variety of conventional catheter shaft materials such as stainlesssteel, or single layer polymeric extrusions of polyethylenes,polyethylene terephthalate, nylon and others well known in the art canbe used. In one embodiment, for example, the tubular body 12 is a PEBAXextrusion having an outside diameter of approximately 0.090 inch.However, the outer diameter can vary between about 0.056 inch forcoronary vascular applications and about 0.150 inch for peripheralvascular applications. Also, because the tubular body 12 must resistcollapse under reasonably anticipated vacuum forces, the foregoingtubular body 12 desirably has a wall thickness of at least about 0.005inch. The wall thickness can, however, be varied depending uponmaterials and design.

[0091] The distal end of the tubular body 12 may be affixed to theproximal end 50 of the cutter housing 21 as shown in FIG. 2 anddescribed above. The proximal end of the tubular body 12 may be affixedto the control 18 as described below.

[0092] With reference to FIG. 9, the point at which the flexible driveshaft 24 is connected to the control 18 is a likely point of damagingbending forces. As such, a reinforcing tube 80 is desirably provided toreduce the likelihood of a failure at that location due to bendingforces. The reinforcing tube 80 may extend from the control unit 18along a proximal portion of the tubular body 12. The reinforcing tube 80preferably extends distally over the tubular body 12 at least about 3 cmand more preferably about 6 cm, and desirably comprises silicone orother conventional biocompatible polymeric material. The illustratedreinforcing tube 80 provides support to avoid over bending and kinkingat the proximal end of the drive shaft 24. With continued reference toFIG. 9, the reinforcing tube 80 may be fastened to the control 18 suchas by interference fit over a snap tip assembly 82 through which theflexible drive shaft 24 and tubular body 12 enter the control 18. Thus,the reinforcing tube 80 advantageously envelops a proximal portion ofthe tubular body 12.

[0093] Respectively, the flexible drive shaft 24 and the tubular body 12operatively connect the cutter 22 and the cutter housing 21 to thecontrol 18 of the illustrated embodiment. With continued reference toFIG. 9, the tubular body 12 and the drive shaft 24 enter the control 18through the snap tip assembly 82. The snap tip assembly 82 may beprovided with a connector, such as a hub 84, having a central lumen incommunication with a vacuum manifold 86. The tubular body 12 may beconnected to the hub 84. Specifically, the hub 84 may snap onto and seala vacuum manifold 86 to the hub 84 and, consequently, to the tubularbody 12. The hub material, therefore, desirably provides long-termmemory for snap-fit tabs that secure this part to the rest of theassembly. The presently preferred hub 84 is injection molded using awhite acetyl such as Delrin. The hub 84 may be rotatable, and may enablethe operator to rotate the tubular body 12 relative to the control 18such that the operator, or clinician, may steer the tubular body 12without having to move the control 18 along with the tubular body 12.Friction to limit this rotation may be provided by a bushing 87 that iscompressed against the hub 84 in the illustrated embodiment.

[0094] The tubular body 12 may be reinforced internally where it passesthrough the hub 84, such as by a thin-wall stainless steel tube (notshown) that extends through and is bonded to the hub 84. In general, agood rotational coupling is desired between the tubular body 12 and thehub. In one embodiment, a portion of the hub bore may be hexagonalshaped, or formed in any other non-circular shape which corresponds to acomplementary shape on the tube to enhance the rotational connectionbetween the hub bore and the tube (not shown). Epoxy or other adhesives(not shown) may also be injected into a space around the stainless steeltube to help prevent the stainless steel tube (not shown) from rotatingrelative to the hub 84. The adhesive also advantageously secures the twocomponents such that the tube (not shown) is less likely to axially pullout of the hub 84.

[0095] With continued reference to FIG. 9, the vacuum manifold 86 ispreferably fastened to a vacuum hose 88 at one outlet and to a motor 90at a second outlet. The hub-end of the vacuum manifold 86 desirablyhouses two silicone rubber O-rings 85 that function as dynamic(rotatable) seals between the manifold 86 and the steel tube (not shown)which extends through the hub 84. The opposite end of the manifold 86,near the proximal end of the drive tube 24, preferably contains a pairof butyl rubber fluid seals 94. These dynamic fluid seals 94 may belubricated with silicone grease. The two fluid seals 94 are mountedback-to-back, with their lips pointing away from each other. In thisconfiguration, the distal seal (i.e., closest to the cutter 22) protectsagainst positive pressure leaks such as may be caused by blood pressureand the proximal seal (i.e., closest to the motor 90) excludes air whenthe system is evacuated and the pressure outside the instrument 10 ishigher than the pressure inside the instrument 10.

[0096] The vacuum manifold 86 may be connected to the motor 90 throughuse of a threaded motor face plate 100. The vacuum manifold 86 ispreferably threaded onto the face plate 100 but may be connected in anysuitable manner. The face plate 100 may be attached to the output end ofthe motor 90 by a threaded fastener 102. The presently preferred motor90 is a modified 6-volt direct-current hollow-shaft, 22 mm outsidediameter motor built by MicroMo.

[0097] In the illustrated embodiment, power is transmitted from themotor 90 to the flexible drive shaft 24 by a length of medium-wallstainless steel tubing that is preferably adhesively-bonded to the driveshaft 24. The tubing forms a transfer shaft 107 and is preferably coatedon the outer surface with approximately 0.001 inch of Type-S Teflon. TheTeflon-coated, exposed ends of the rigid drive shaft, or transfer shaft107, provide a smooth wear-surface for the dynamic fluid seals discussedabove. The transfer shaft tubing may be hypodermic needle stockmeasuring approximately 0.036 inch inside diameter by 0.053 inch outsidediameter, before coating. The transfer shaft 107 desirably is slip fitthrough the approximately 0.058 inch inside diameter of the hollow motorshaft, and desirably extends beyond the length of the motor shaft inboth directions. The slip fit advantageously accommodates axial slidingmovement of the transfer shaft 107 relative to the motor 90 and thebalance of the instrument 10. Thus, axial movability may beaccommodated.

[0098] The drive shaft 24 is advantageously capable of axial movementrelative to the motor 90 as described above. Controlled axial movementof the drive shaft 24, and ultimately the cutter 22 and its connectedcomponents, is desirable regardless of the mechanical connectionallowing such movement. The movement allows the cutter 22 and, in someembodiments, the drive shaft 24 to be withdrawn proximally duringplacement of the catheter sheath, or tubular body 12, in thevasculature. Following positioning, the cutter 22 may then be advancedforward into a cutting position. Such a configuration allows increasedmaneuverability and flexibility during positioning and easier trackingthrough the vasculature. This configuration also allows for easiersterilization of the outer tubular body 12 in a compact coiled package.However, as will be recognized by those of skill in the art, suchrelative axial movement of the cutter 22 and the tubular body 12 is notnecessary for utilization of various other aspects and advantages of thecurrent invention.

[0099] A small drive plate 103, bonded to the rear end of the transfershaft 107, advantageously couples with a drive sleeve 105 that isattached to the approximately 0.078 inch outside diameter motor shaft92. The drive plate 103 may be any of a number of geometricconfigurations. Preferably, the drive plate 103 is a rotationallysymmetrical shape having a central aperture although otherconfigurations may also be used. The symmetry facilitates rotationalbalancing. In one embodiment, the drive plate 103 is square with acentral aperture, triangular with a central aperture, or circular with acentral aperture, with a connecting member to tie the drive plate to thedrive sleeve with a reduced likelihood of slippage. Together, the driveplate 103 and the drive sleeve 105 form a concentric drive coupling,similar to a spline connection, between the motor shaft 92 and thetransfer shaft 107.

[0100] The transfer shaft 107, in turn, may be connected to the flexibledrive shaft 24. The concentric drive coupler configuration preferablyallows approximately 0.25 inch of relative longitudinal movement betweenthe drive plate 103 and the drive sleeve 105, which is sufficient toaccommodate thermal and mechanical changes in the relative lengths ofthe outer tube 12 and flexible drive tube 24. An integral flange on thedrive plate 103 or the drive sleeve 105 may serve as a shield to deflectfluid away from the rear motor bearings in the event of a leaking fluidseal. Thus, the drive sleeve 105 is preferably a solid walled annularflange which acts as a tubular deflection as will be understood by thoseof skill in the art.

[0101] The drive sleeve 105 and the drive plate 103 are preferablymolded from Plexiglas-DR, a medical-grade, toughened acrylic resin madeby Rohm and Haas. These parts have shown little tendency to crack in thepresence of the chemicals that might be present or used in the assemblyof the device; these chemicals include cyanoacrylate adhesives andaccelerators, motor bearing lubricants, alcohol, epoxies, etc. The drivesleeve 105 and the drive plate 103 are also preferably lightlypress-fitted to their respective shafts 92, 107, and secured with afillet of adhesive applied to the outside of the joints.

[0102] With continued reference to FIG. 9, an infusion manifold 108 maybe arranged at the proximal end of the control 18. The infusion manifold108 is preferably designed as an input circuit; thus any fluid that canbe pumped or injected at a pressure exceeding the diastolic pressure inthe artery or vein could be used, but saline solutions, therapeuticdrugs and fluoroscope contrast media are most likely to be used withthis device. For instance, saline solutions may be used to purge airfrom the tubular body 12 and drive tube 24 before performing proceduressuch that air embolism may be avoided, and may also be used during anatherectomy procedure to provide a continuous flow of liquid (other thanblood) during cutting to help carry debris through a return circuit. Aswill be recognized, the device 10 generally is purged of air prior toperforming procedures. In such a case, an infusion pump or elevated IVbag may be used to ensure a continuous, low-pressure flow of salinesolution through the system, depending upon the application andprocedure.

[0103] At various times during a procedure, the clinician may requestthat a bolus of contrast medium be injected into the instrument 10 toenhance a fluoroscopic image of the artery or vein, either to positionor to direct the guidewire 28, to locate a blockage, or to confirm thata stenosis has indeed been reduced. Contrast medium is a relativelydense material and high pressure (usually several atmospheres) isusually required to force the material quickly through the small,elongated lumen 26 of the drive tube 24. Such a medium may be infusedusing an infusion pump, for instance.

[0104] In the case of the illustrated surgical instrument 10, theinfusion manifold 108 may be comprised of several components. The firstcomponent may be an infusion port that may contain a medical infusionvalve 109, such as that supplied by Halkey-Roberts Corp. This siliconerubber check valve assembly 109 is preferably designed to be opened byinsertion of a male Luer-taper (or lock) fitting. The valve 109 morepreferably stays open as long as the taper fitting remains in place, butdesirably closes immediately if it is withdrawn. This action providessimple access when needed, but provides the required backflow protectionto minimize loss of blood through this route.

[0105] The infusion valve 109 is preferably permanently bonded into aside arm of a flush port manifold 111, an injection-molded, transparentacrylic fitting. The flush port manifold 111 desirably has an integralthreaded extension that may protrude from the proximal side of thecontrol 18. The threaded extension may be provided with a siliconeguidewire seal 113, and an acetyl (Delrin) guidewire clamp nut 112 thattogether function as a hemostasis valve compression-fitting. Delrin maybe used for the clamp nut 112 to minimize stiction and galling of thethreads during use. Note that the materials indicated for thecompression-fitting may be varied as will be recognized by those ofskill in the art. An internal shoulder on the threaded portion of thenut 112 advantageously acts as a position stop, preventing extrusion ofthe seal 113 that might otherwise result from over-tightening. Theguidewire 28 desirably extends through both the seal 113 and the nut112.

[0106] When the clamp nut 112 is tightened, the guidewire seal 113 maycompress against the guidewire 28 to lock it in place and to preventleakage of blood or air through the seal 113. When it is necessary toslide the guidewire 28, or to slide the surgical instrument 10 along theguidewire 28, the clamp nut 112 is first loosened to reduce the clampingaction somewhat and the relative movement is then initiated. If noguidewire 28 is used, the seal 113 may compress against itself and closeoff the passageways to reduce or prevent leakage.

[0107] A fluid channel advantageously extends through the flush portmanifold 111, continuing through the open lumen of the drive tube 24,through a distal aperture 39 in the distal extremity of the cutter 22.The guidewire 28 preferably follows the same path. A leak-proofconnection between the flush port manifold 111 and the drive tube 24 istherefore desirable.

[0108] Accordingly, a flush port flange 106 may be bonded to the motorend of the flush port manifold 111, creating a chamber housing a lowdurometer butyl rubber lip seal 114. The flange 106 may be manufacturedof molded acrylic or the like. The lip seal 114 forms an effectivedynamic seal against one end of the transfer shaft 107. Lip seals arepressure-compensating devices that function at zero or low pressure bylight elastomeric compression against a shaft, minimizing the dragcomponent in a dynamic application. When pressure against the sealincreases, the lip tightens against the shaft, increasing both thesealing action and the dynamic friction. In this application, however, ahigh pressure sealing requirement preferably is only encountered duringinjection of contrast medium, typically when the cutter 22 is notrotating. Lower pressure dynamic sealing may be required during salineinfusion, however, so pressure compensating lip seals are presentlypreferred.

[0109] The lip seal 114 is desirably transfer-molded butyl rubber, withabout a 0.047 inch inside diameter lip (generally within the range offrom about 0.035 inch to about 0.050 inch), running on the transfershaft 107, which may have an outside diameter of approximately 0.055inch. Medical-grade silicone grease may be used lubricate the interfacebetween the lip seal 114 and the transfer shaft 107, but the greasetends to be forced away from the lip during prolonged use. Thus, aTeflon coating on the transfer shaft 107 may act as a back-up lubricantto reduce or eliminate seal damage in the event the grease is lost.

[0110] Returning to the vacuum manifold 86, as illustrated in FIG. 9,the vacuum hose 88 may be attached to the remaining port of the Y-shapedvacuum manifold 86. The hose 88 may be attached in any suitable manneras will be appreciated by those of ordinary skill in the art. The vacuumhose 88 generally extends between the vacuum manifold 86 of the control18 and a vacuum source (see FIG. 1) such as a house vacuum of thecatheter lab of a hospital or a vacuum bottle.

[0111] The vacuum hose 88 desirably extends through a switchconfiguration 120 described in detail below. In the illustratedembodiment, the vacuum hose 88 then further extends to the bottomportion of the control 18. A pinch resistant sleeve 116 may be providedto prevent the pinching of the vacuum hose 88 as it exits the control18. Additionally, the pinch resistant sleeve 116 provides a liquid sealto further reduce the likelihood of liquids entering the control 18 unitduring operation.

[0112] In interventions such as those with which the present surgicalinstrument 10 has particular utility, it has been discovered to bedesirable that cutting should occur only under sufficient aspiration.Accordingly, an aspect of the present invention involves a cutterlock-out mechanism that will not allow cutting of material unlesssufficient aspiration is present. The aspiration rate may be directlysensed (i.e., flow monitoring) or indirectly sensed (i.e., vacuummonitoring). For instance, because the level of vacuum will typically beone determining factor of the level of aspiration, the vacuum level maybe monitored to determine when a new vacuum bottle should be employed.In such a situation, if the level of a sensed vacuum drops below about15 inches Hg, insufficient clearing vacuum is present and the risk ofblockage within the device 10 increases. Thus, a cutter lock-outmechanism should be employed to prevent cutting of material until thevacuum level is replenished. Specifically, it has been determined that asensed vacuum of about 13.5 to about 14 inches Hg usually precedesclogging in the illustrated embodiment.

[0113] The cutter lock-out mechanism is generally comprised of twocomponents, either of which may find utility individually or incombination. One of the components is a vacuum monitor. The vacuummonitor (not shown) is desirably a linear pressure transducer thatsenses the presence of an adequate vacuum force. The signal from thetransducer is preferably utilized to enable an automatic override of themotor such that the motor cannot turn the cutter 22 if the vacuum dropsbelow a threshold level (e.g. 15 inches Hg). Generally, the vacuummonitor may also comprise a vacuum detector, a comparator of anysuitable type, an alarm or circuit cut-out. Thus, the vacuum detectormay sample the state of operation of the vacuum, the comparator maydetermine varying operating conditions, and if the vacuum force dropsbelow or unexpectedly and suddenly exceeds the pre-set threshold levelfor any reason the alarm can alert the operator to take correctiveaction, and/or the cut-out circuit can automatically stop rotation ofthe cutter.

[0114] The cutter lock-out mechanism may also comprise a flow monitor(not shown). The flow monitor may be of any suitable type and may simplymonitor the flow rate, or aspiration rate, through the aspirationchannel. The flow monitor also may be connected to circuitry or alarmssuch that the user may be warned if the aspiration rate slows (i.e.,conditions indicative of a blockage arise) and/or such that the device10 may automatically take corrective action when a decrease in theaspiration rate is detected. For instance, the device 10 may disablecutting (i.e., rotation of the cutter 22), increase the suction level orotherwise attempt to auto-correct the situation. Also, it is anticipatedthat various alarms, be they visual, tactile or auditory, may beutilized to inform the operator or clinician of the alert status.

[0115] Another component of the cutter lock-out mechanism is a switcharrangement that advantageously controls the motor state and vacuumapplication as described below. As will be recognized by those of skillin the art, such a switch may be mechanical, electromechanical, orsoftware-controlled. With reference to FIGS. 9A-9C, a schematicallyillustrated switch configuration 120 desirably assures that the motor 90driving the rotatable drive shaft 24, which in turn drives the cutter22, may not be activated unless the vacuum is being applied. Theillustrated pinch valve switch 120 generally comprises a push buttonoriented along the Z axis shown in FIG. 10A. The switch push button 124may translate along the Z axis when depressed by the user. Desirably,the lower portion of the push button 124 is provided with a u-shaped cutout forming a tunnel along the x-axis. The cut out is preferably sizedto correspond to a compression spring 126 extending therethrough. Thepresently preferred compression spring 126 is a precision-lengthstack-wound button spring fabricated from 0.027″ diameter 302 stainlesssteel wire, with a closed retainer loop at one end. The push button 124may be positioned along a portion of the compression spring 126 suchthat the push button 124 rests on the compression spring 126 and issupported in an up position. The switch push button 124 thus can travelto a down position when depressed by the operator to a position such asthat shown in FIG. 10B. The compression spring 126 provides a bias suchthat the push button 124 will return to the up position when released.Of course, any other suitable biasing mechanism or component may also beused.

[0116] The switch push button 124 may be further provided with an axialarm 128 that preferably extends in a direction perpendicular to thedirection of travel of the push button 124. Thus, in some embodiments,the arm may assume an “L” shaped configuration. It is anticipated that avariety of arm configurations may also be employed.

[0117] An electronic switch 130 is desirably located below the axial arm128 of the switch push button 124. Thus, as the push button 124 isfurther depressed beyond the position in FIG. 10B, to a position such asthat illustrated in FIG. 10C, contact is made on the electrical switch130. The electrical switch 130, when closed, allows current to flow froma power source 122 to the motor 90. Thus, depression of the push button124 creates a flow of current that drives the motor 90. The motor 90drives the drive tube 24 and cutter 22 of the present surgicalinstrument 10 as described above.

[0118] Advantageously, the compression spring 126 is also preferablyattached to a pinching member 132 of the switch configuration 120. Asthe push button 124 is depressed, the compression spring 126 isadvantageously initially deflected. Desirably, the deflection in thecompression spring 126 causes the pinch member 132 to retract. Thus, thepinch member 132 is retracted once the push button 124 is depressed. Asthe pinch member 132 is retracted, a vacuum is initiated and aspirationflow is allowed to pass the pinch valve 120. Advantageously, the amountof flow past valve may depend on how far the button 124 is depressed,enabling control of the amount of suction (and, thereby, the level ofaspiration) if desired. Further depression of the push button 124 beyondthe retraction point initiates a contact of the electrical switch 130and, therefore, allows the motor 90 to be powered only after the vacuumflow has begun.

[0119]FIG. 10A illustrates a relaxed, non-depressed condition in whichthe vacuum hose 88 is closed by the pinch valve 132 and the spring 126,and the electrical switch 130 which controls power supply to the motor90 is open. With reference to FIG. 10B, the push button 124 is partiallydepressed, thereby causing the vacuum hose 88 to be opened whilemaintaining the electrical switch 130 open. Further depression of thepush button 124, illustrated in FIG. 10C, closes the electrical switch130 while the vacuum hose 88 is maintained in an open state. Thus,depressing the push button 124 an initial amount starts the vacuum firstand further depression initiates the cutting action. Such timing reducesrisks associated with cutting without aspiration. Because repeatedcycles of opening and closing the valve may tend to shift the positionof the tube 88, internal ribs (not shown) are preferably provided in thecontrol 18 to maintain the proper position of the tube 88.

[0120] A return flow path of the illustrated device 10 for aspirationand the like starts at the cutter 22, passes through the helical thread46 and the cutter blocks 42 of the cutter 22 (and stationary blocks ofthe cutter housing, if present), continues through the outer lumen 20 ofthe outer tube 12 to the vacuum manifold 86, and then passes through alength of vacuum tubing 88 to a tissue collection/fluid separationcontainer, such as a vacuum bottle. The return flow may be assisted by apositive vacuum supply, such as the vacuum bottle or a house vacuum, asis known in the art. For instance, the collection container may beconnected to a vacuum collection canister that may be, in turn, hookedto a regulated central vacuum source or a suction collection pump orevacuated container.

[0121] The pinch valve assembly is preferably designed with a “shippinglock-out” feature (not shown) that secures the button 124 in a partiallydepressed position where the vacuum tube 88 is no longer compressed, butthe switch 130 is not yet actuated. This preserves the elastic memory ofthe pinch tube and protects the device from accidental actuation duringhandling or storage. In its present form, a thin, flexible lock-out wirewith an identifying tag (not shown) can be inserted at the last stage ofinstrument manufacturing, passing through a hole in the button (notshown) and extending through a notch in the side wall of the control 18.In this configuration, a highly-visible tag protrudes from the side ofthe control 18, preventing use of the device until the wire is pulledfree. Removing the lock-out wire releases the button 124 and returns thecontrol 18 to a functional condition. Once removed from the originallocked position, the lock-out wire (not shown) desirably cannot bereinserted without disassembly of the control 18.

[0122] With reference again to FIG. 9, the device 10 is preferablycontrolled by electronic circuitry such as may be contained on a printedcircuit board 133. The circuitry providing the power to the motor 90 mayalso include a circuit to check the load on the motor. An exemplarymotor control and feedback circuit is illustrated in FIG. 11; however,as will be readily recognized by those of ordinary skill in the art,many other motor control circuits may also be implemented. As is known,when a direct current motor, as used in this invention, encountersresistance to rotational movement, an increased load is placed on thepower source 122. Accordingly, as described below, the circuitry isprovided with the capability to identify, indicate, record and possiblycompare the speed and/or torque to previously recorded speeds ortorques. Specifically, the speed and/or torque, as indicated by thelevel of current to the motor, may be compared over time through the useof a comparator. Additionally, a reverse switch may be provided toreverse out of jams or potential jams when necessary. Such a reverseswitch may be a momentary switch or any other suitable switch as will berecognized by those of skill in the art.

[0123] As described below in detail, a motor controller 134 preferablyprovides the motor 90 with sufficient energy by using a combination ofmissing pulse and pulse width modulation. For instance, the motor speedmay be sensed by measuring the back electromotive force (EMF), which isproportional to speed. A portion of the back EMF may be fed to thecontroller 134, which preferably varies the drive power to the motor 90to maintain a constant speed. The circuit values of the controller 134allow motor speed settings of about 1,000 RPM to about 8,000 RPM. Thespeed chosen for no load operation in one embodiment may preferablyrange from approximately 1,500 RPM to about 5,000 RPM. In a presentlypreferred embodiment, the no load operation speed is approximately 2,000RPM. Desirably, the motor speeds associated with the present inventionare less than those associated with abrasive-type devices andturbulence-based devices as will be recognized by those of skill in theart. In some embodiments, the motor control circuitry may limit themotor torque to a range of about 0.10 oz-inches to about 0.45 oz-inchesby sensing the motor current and setting the motor drive power to theappropriate level. A switching controller, thus, may be used for tworeasons: (a) it is very efficient—it uses less than 0.015 amperes (themotor current would vary from 0.05 to 0.4 amperes, or perhaps more), and(b) it can deliver appropriate torque instantly or on demand, even atlow motor speeds, so the likelihood of stalling is minimized.

[0124] The power source 122, preferably a 9-volt battery, may not beelectrically connected to the controller 134 until the push button 124is depressed, as discussed above, so standby power drain isadvantageously eliminated or reduced. In the illustrated embodiment, alight emitting diode (LED) is desirably on when the motor is running atnormal loads (i.e., the sensed current level is lower than apredetermined current level requiring an alert). This LED may be greenin some embodiments and will be referred to as such in connection withthe illustrated embodiment. Another LED turns on at a motor current ofapproximately 0.25 amperes, or another threshold level that may indicatea motor “overload” situation. This LED may be red in some embodimentsand will be referred to as such in connection with the illustratedembodiment. For instance, the red LED may indicate that the current isproximate, or has achieved, a predetermined maximum safe value. Thepreset maximum safe value is the upper limit, as determined by thespecific design and configuration of the device 10, for current thatindicates an overload condition. Thus, another feature of the presentinvention includes the ability to provide feedback to the operator basedupon motor load. This is advantageous in that the operator can bealerted to a potential binding of the instrument and react accordingly.For instance, the progression rate of the instrument may be reduced orstopped or the instrument may be backed from the trouble location usingthe reverse switch or otherwise. It should also be understood that thedevice may make automatic adjustments to the motor speed relative to thesensed load utilizing methods which would be readily apparent to oneskilled in the art following a review of FIG. 11.

[0125] Any of a variety of tactile, auditory or visual alarms may alsobe provided either in combination with, or as alternatives to, eachother and the LEDs. For instance, the surgical instrument could vibrateor provide an audible signal when it encounters an overload situation.The pulses or tones may vary to correspond to any variance in resistanceto rotation. For example, the pitch may increase with resistance or thespeed of a repeating pulse of sound may increase. Additionally, where a(CRT) monitor is used to visualize the operation, a visual signal couldbe sent to the monitor to display the operating characteristics of thesurgical equipment. As will be further recognized to those skilled inthe art, other variations of alerting the operator to the operatingcharacteristics of the present invention may be provided.

[0126] The present invention thus provides feedback to the clinician inreal time during the progress of the rotational atherectomy procedure.Real time feedback can allow the clinician to adjust the procedure inresponse to circumstances that may vary from procedure to procedure,thereby enhancing the overall efficiency of the procedure and possiblyminimizing additional risks such as the creation of emboli. Pressing thecutter 22 into a lesion with too much force may produce an increasedload, which can then be detected by the circuitry 131 and communicatedto the clinician in any of a variety of ways as has been discussed. Thismay allow the clinician to ease back on the distal advancement forceand/or adjust the vacuum or RPM of the cutter 22, such as by reducingthe advancement force and lowering the resistance to rotation of thecutter 22, until the load is reduced to an acceptable level, andcontinue with the procedure. As will be recognized, if aspiration dropsdue to increased material being aspirated, the load is likely to haveincreased; therefore, the clinician is alerted to such an increase inload such that corrective action may be taken. By allowing the load toreturn to an acceptable level, the aspiration rate may also return to anacceptable level in some embodiments. As will be recognized, the loadmay increase due to a blockage and the blockage would lower theaspiration rate; however, clearing the blockage will generally returnthe aspiration rate to a desired level as well as reduce the load on themotor.

[0127] In addition, increased load can be incurred by kinks at anylocation along the length of the instrument, thereby reducing the motorspeed. Kink-originated loading could be reflected in the feedbackmechanism to the clinician, so that the clinician can assess whatcorrective action to take.

[0128] Another aspect of the present invention involves a selectivelyreversible tip rotation. For instance, the drive motor may be reversedsuch as by manipulation of the reverse control switch (not shown) on thehandle of the control 18. Motor reversing circuitry, with or without avariable speed control, is well understood by those of skill in the art.Momentary reversing of the direction of rotation of the distal cutter,most likely at a relatively low speed of rotation, may be desirable todislodge material which may have become jammed in the cutter tip. Inthis manner, the clinician may be able to clear a cutter tip blockagewithout needing to remove the catheter from the patient and incur theadditional time and effort of clearing the tip and replacing the device.Low speed reverse rotation of the cutter may be accomplished incombination with a relatively increased vacuum, to reduce the likelihoodof dislodging emboli into the blood stream. Following a brief period ofreverse rotation, forward rotation of the cutter tip can be resumed.Whether the obstruction has been successfully dislodged from the cuttertip will be apparent to the clinician through the feedback mechanismsdiscussed above. Moreover, it is anticipated that the device mayalternatively have substantially the same torque, speed, vacuum force,and alarm thresholds when the cutter is rotated in either direction. Itis, however, presently preferred to utilize the same speed of rotationin both forward and reverse rotation.

[0129] In the presently preferred embodiment of the control and powersupply circuitry illustrated in FIG. 11, the motor controller has anLM3578A switching regulator, indicated generally by U1 in FIG. 11. Theswitching regulator may be an LM3578A switching regulator in someembodiments; one of ordinary skill in the art will readily recognizeother components and circuitry that can perform essentially the samefunctions. The switching regulator is normally used as a power supplyregulator, wherein it may provide a substantially constant voltageregardless of load. A negative in jack (pin 1) may be used as an errorinput. For instance, when the voltage at pin 1 is less than about 1volt, an inference may be established that the motor speed may be toolow, therefore the output jack (pin 6) goes low. When the output at pin6 goes low, it may cause a gate (pin G) of Q1 to be near 0 volts. Aswill be recognized, this may cause Q1 to turn on with a resistance ofabout 1.3 ohms in the illustrated embodiment. Advantageously, the endresult is that the motor, Q1, D1 and R4 may be connected in seriesacross the battery. The motor current will likely be rather heavy, sothe motor speed may increase. This “on” condition lasts for a time thatis preferably controlled by U1's oscillator, whose frequency (about 500Hz) may be set by C4. Also, the switching regulator U1 desirably limitsthe output on time to about 90% of this 2-millisecond period(1/frequency=period) because it uses the first 10% portion purely forcomparing the error signal to the reference. The comparisonadvantageously continues during the 90% period, with the output on oroff as determined by the error signal. If the motor speed were toincrease to the proper level during the 90% portion of the cycle, theoutput would preferably shut off immediately, thereby resulting in anarrowed pulse. Hence, pulse width modulation is achieved.

[0130] Desirably, the output of the switching regulator U1 only goeslow, so R1 preferably pulls the output high when the switching regulatorU1 is off. R13 isolates the switching regulator U1 from the gatecapacitance of Q1, thereby advantageously ensuring a more reliablestart-up of the switching regulator U1 upon application of power. D1preferably prevents below-ground motor switching transients fromreaching the transistor Q1. In the illustrated embodiment, the VP2204may have a 40-volt rating, which advantageously provides plenty ofmargin for withstanding voltage transients. As will be recognized bythose of skill in the art, any other suitable control circuit may alsobe utilized. Power supply filter C5 preferably helps provide the largeshort duration currents demanded by the controller, especially when thebattery power is nearly depleted.

[0131] In the illustrated embodiment, an N-channel FET, indicated byreference numerals Q2, preferably switches the motor's back EMF to astorage capacitor C2 during the portion of the control cycle when themotor is not powered (i.e., Q2 is off when Q1 is on, and vice versa).The resistor R2, along with the gate capacitance of the FET Q2,advantageously forms a delay network so that when the FET Q2 turns onafter the FET Q1 turns off. This configuration may block turn-offtransients and may present a voltage to C2 that more accurately reflectsthe back EMF. The FET's Q2 turn-off need not be delayed, so D2 may turnon with negative-going signals and may parallel the resistor R2 with alow impedance, thereby giving only a slight delay. A resistor R5 and aresistor R6 preferably divide the back EMF to provide the error voltage(nominally about 1 volt) to pin 1 of the switching regulator U1. Thevalue of the resistor R5 desirably determines the level of back EMF,and, therefore, the motor speed required to produce about 1 volt at theswitching regulator U1, pin 1.

[0132] The resistor R4 may be in series with the motor and may be usedto sense the motor current and limit the motor torque accordingly. Forinstance, the current pulses through the resistor R4 generate voltagepulses, which may be integrated (averaged) by the resistor R3 and thecapacitor C1 and fed to pin 7 of the switching regulator U1, which isthe current limit input. Preferably, when the voltage at this pin isabout 0.110 volts or more, the switching regulator U1 may not increasethe output drive, regardless of the error voltage. The circuit valuesshown result in about 0.45 amp average, or between about 0.45 and about0.5 oz-in. of stall torque for the motor.

[0133] The back EMF voltage stored by the capacitor C2 is preferablyfurther filtered by a resistor R7 and a capacitor C3 and may appear atthe output (pin 7) of an amplifier (U2) as a relatively noise-freesignal which follows the motor speed with a slight time lag. Theamplifier in the illustrated embodiment is an LM358 buffer amplifier.The voltage is desirably divided by a resistor R8, a resistor R9 and aresistor R10 and may appear at the positive input of the comparatorsection of the amplifier U2 (pin 3). A negative input is desirably fixedat about 1 volt, since it is connected to the switching regulator U1,pin 2. When the voltage at pin 3 exceeds that at pin 2, the output (pin1) is high and the green (Cutting) LED is on in the illustratedembodiment. When the voltage at pin 3 is less than at pin 2, the outputis low and the red (Overload) LED is on in the illustrated embodiment.“Overload” in the embodiment being described herein has been defined asthe point when the motor current reaches about 70% of stall current;however, any desired percentage of stall current may be used to definean overload condition. The value of a resistor R9 determinesapproximately equal red and green LED intensities with a dynamic motorload that causes a motor current of approximately 0.35 amperes.

[0134] With continued reference to FIG. 11, a test connector P2 providessignals and voltages for production testing of the controller board,which may be tested as a subassembly prior to installation. The testconnector P2 may also be accessible when the top half of the housing isremoved, such as for testing at higher levels of assembly. It should beappreciated that one of skill in the art may modify the test connectorand related circuitry such that the connector could also become a databus all data to be passed from the control to a recorder, a display orthe like.

[0135] In a presently preferred method of use, a guidewire 28 is firstpercutaneously introduced and transluminally advanced in accordance withwell known techniques to the obstruction to be cleared. The surgicalinstrument 10 is then introduced by placing the distal end 16 of theflexible tubular body 12 on the guidewire 28, and advancing the flexibletubular body 12 along the guidewire 28 through the vessel to thetreatment site. When the distal end 16 of the flexible tubular body 12has been maneuvered into the correct position adjacent the proximalterminus of material to be removed, the drive tube 24 is rotatedrelative to the tubular body 12 to cause the cutter 22 to rotate in adirection which will cause the forward end 47 of the thread 46 to drawmaterial into the housing 21. A circular cutting action may be providedby mutual cooperation of the outer cutting edge of the screw thread 46with lip 39 of the cutter housing 21 and the internal peripheral wall ofthe cutter housing 21. In addition, the cutter housing 21 in cooperationwith the flanges 42 and any other stationary members present,effectively chops or minces the strands of material being drawn into thecutter housing 21. The cut material is then carried proximally throughthe annular passageway between the flexible drive tube 24 and thetubular body 12 under the force of vacuum. If an increase in load and/ordecrease in RPM is detected, the clinician can take reactive measures asdescribed above. The vacuum preferably pulls the cuttings through theentire length of the lumen 20 and vacuum tube 88 and into a suitabledisposal receptacle. A manual or automatic regulator may regulate thevacuum source such that a constant flow velocity may be maintained, orblockages reduced or cleared, through the vacuum tube 88 regardless ofthe viscosity of the material passing through the vacuum tube 88.

[0136] With reference now to FIG. 12, a further aspect of the presentrotational atherectomy device will be described in detail. Asillustrated, the elongate flexible member 12 preferably includes anexpandable component 150 near the distal end 16 of the flexible member12. More preferably, the expandable component 150 is positionedproximate the cutter housing 21 at a location directly adjacent theproximate end of the housing 21. In some embodiments, the expandablemember 150 may be positioned on the housing 21 itself.

[0137] The expandable member 150 preferably extends about only a portionof the total circumference of the flexible member 12. In this regard,the expandable member is used to offset the cutter tip 22 such that theaxis of rotation of the cutter tip is disposed about a second axis thatis generally parallel to an axis of the artery in which the device isdisposed but the cutter tip axis is laterally displaced from the axis ofthe artery. Specifically, as the expandable member 150 is inflated, orexpanded, the expandable member 150 contacts one of the sides of theartery, thereby displacing the flexible member 12 and the cutter tip 22in a radial direction away from the center of the artery. In theillustrated embodiment, the expandable member 150 extends about 75°around the circumference of the flexible member 12. In otherembodiments, the expandable member may extend around between about 45°to about 270°.

[0138] The expandable member may comprise any of a number of components.For instance, the illustrated expandable member is a Pellethane balloonhaving eccentric tails 152. The presently preferred material,Pellethane, forms a compliant balloon that allows the diameter to growwith increases in inflation pressure. The preferred variant ofPellethane is 2363-90AE which allows a working pressure of between about10 psi and about 60 psi with diameter growths of between about 1.5 mm toabout 2.0 mm. Of course, other materials may be chosen depending uponthe application. In other embodiments, the working pressure may rangefromabout 5 psi and about 50 psi with diameter growths of between about0.8 mm and about 3.0 mm. The inflatable portion of the balloonpreferably has an axial length of between about 8 mm and 2 mm with amore preferred length being about 5 mm. In arrangements having aninflatable length of about 5 mm, it is anticipated that about 3 mm ofthe balloon will be useful in offsetting the cutter tip 22 relative toan axis of the lumen in which the cutter tip 22 is disposed.

[0139] The eccentric tails 152 of the balloon also form a part of thepresently preferred arrangement. The eccentric tails 152 generally lieflat along the flexible member 12 to which they are attached. Such anarrangement allows the deflated profile of the device 10 to be decreasedas well as eases the bonding between the expandable member 150 and theflexible member 12. While concentric tailed balloons may adequatelyfunction as the expandable member 150, the eccentric tailed balloons arepresently preferred. The tails are preferably adhered to the flexiblemember with an epoxy resin or ultraviolet adhesive. In somearrangements, the tails 152 are preferably captured by external rings,housings or tubes.

[0140] An inflation lumen 154 extends between the expandable member 150and a portion of the device 10 which is external to a patient. The lumen154 may be formed within the flexible member 12 or may be positioned tothe outside of the flexible member 12. The positioning of the inflationlumen 154 may be selected as a result of the application in which thedevice 10 will be used.

[0141] In use, the device 10 featuring the balloon operates in a similarmanner to the device 10 described above. Specifically, as describedabove, the guidewire 28 is first percutaneously introduced andtransluminally advanced in accordance with well known techniques to theobstruction to be cleared. The surgical instrument 10 is then introducedby placing the distal end 16 of the flexible tubular body 12 on theguidewire 28, and advancing the flexible tubular body 12 along theguidewire 28 through the vessel to the treatment site. When the distalend 16 of the flexible tubular body 12 has been maneuvered into thecorrect position adjacent the proximal terminus of material to beremoved, the expandable element is inflated with a fluid in a knownmanner. The expandable member 150 acts as a deflecting mechanism tooffset the cutter tip 22 from the centerline of the artery.

[0142] At this point, any of at least two modes of operation may beused. In a first mode, illustratedschematically in FIG. 13, the drivetube 24 is rotated relative to the tubular body 12 to cause the cutter22 to rotate in a direction which will cause the forward end 47 of thethread 46 to draw material into the housing 21. Also,suction may be usedto pull material into the housing 21. A circular cutting action may beprovided by mutual cooperation of the outer cutting edge of the screwthread 46 with lip 39 of the cutter housing 21 and the internalperipheral wall of the cutter housing 21. In addition, the cutterhousing 21 in cooperation with the flanges 42 and any other stationarymembers present, effectively chops or minces the strands of materialbeing drawn into the cutter housing 21.

[0143] The cutter tip 22 is then rotated in an eccentric rotation byturning the flexible member 12 while the cutter tip 22 is spinning inthe housing 22. In one arrangement, the cutter tip is eccentricallyrotated through a pass of about 360°; however, the sweep of the cuttertip may be varied depending upon any one of a number of factors. Also,the rotation of the flexible member 12 may be performed manually. Aftera complete rotation of the flexible member 12, the cutter tip 12 is thenadvanced forward through another portion of the material to be removed.The cut material is carried proximally through the annular passagewaybetween the flexible drive tube 24 and the tubular body 12 under theforce of vacuum. If an increase in load and/or decrease in RPM isdetected, the clinician can take reactive measures as described above.The vacuum preferably pulls the cuttings through the entire length ofthe lumen 20 and vacuum tube 88 and into a suitable disposal receptacle.A manual or automatic regulator may regulate the vacuum source such thata constant flow velocity may be maintained, or blockages reduced orcleared, through the vacuum tube 88 regardless of the viscosity of thematerial passing through the vacuum tube 88.

[0144] In another mode of operation, illustrated schematically in FIG.14, the cutter tip 22 is axially advanced through the material to beremoved after the deflecting expandable member 150 is inflated. Acircular cutting action may be provided by mutual cooperation of theouter cutting edge of the screw thread 46 with lip 39 of the cutterhousing 21 and the internal peripheral wall of the cutter housing 21. Inaddition, the cutter housing 21 in cooperation with the flanges 42 andany other stationary members present, effectively chops or minces thestrands of material being drawn into the cutter housing 21. The cutmaterial is carried proximally through the annular passageway betweenthe flexible drive tube 24 and the tubular body 12 under the force ofvacuum. If an increase in load and/or decrease in RPM is detected, theclinician can take reactive measures as described above. The vacuumpreferably pulls the cuttings through the entire length of the lumen 20and vacuum tube 88 and into a suitable disposal receptacle. A manual orautomatic regulator may regulate the vacuum source such that a constantflow velocity may be maintained, or blockages reduced or cleared,through the vacuum tube 88 regardless of the viscosity of the materialpassing through the vacuum tube 88.

[0145] After the cutter tip 22 has traversed the length of the materialto be removed, the cutter tip 22 is withdrawn through substantially thesame path of axial travel through the material. The expandable member150 is then deflated and the flexible member 12 is reoriented for asecond pass through the material. In some arrangements, the expandablemember 150 may remain inflated or may be partially deflated duringreorientation. The flexible member 12 may be rotated to any degreedesired by the operator. In one arrangement, the flexible member 12 isrotated about 60degrees from the first pass. This arrangement isillustrated schematically in FIG. 14. The expandable member 150 is theninflated and the cutter tip 22 is again axially advanced through thematerial to be removed. This process is repeated as desired in anyparticular application. In the illustrated arrangement, a non-offsetpass is also performed such that the cutter tip 22 passes through agenerally central location. One of ordinary skill in the art willreadily recognize that the degree of overlap between passes may varyfrom operator to operator. Also, in instances in which the overlap isnot extensive, the paths formed by the individual passes may coalesceinto a single lumen.

[0146] As will be recognized, either of the above described modes ofoperation will result in an enlarged effective flow path as compared tothe outside diameter of the device. It should be recognized that anycombination of the modes of use of the deflection expandable memberdiscussed directly above may also be used. The off-center cuttingarrangement advantageously implements the device 10 in an operationwhich enlarges the diameter of the cleared material over and above theoutside diameter of the catheter being used to house the cutter.

[0147] Although this invention has been described in terms of certainpreferred embodiments, other embodiments apparent to those of ordinaryskill in the art are also within the scope of this invention.Accordingly, the scope of this invention is intended to be defined onlyby the claims that follow.

What is claimed is:
 1. A rotational medical device comprising: anelongate flexible tubular body, having a proximal end and a distal end;a rotatable element extending through the body; a rotatable tip at thedistal end of the body and connected to the rotatable element; a controlon the proximal end of the body; at least one radially inwardlyextending stationary cutting member on the tubular body; and at leastone radially outwardly extending flange on the rotatable tip forcooperating with the stationary cutting member to cut material drawninto the tubular body.
 2. A rotational medical device as in claim 1,comprising two radially outwardly extending flanges on the tip.
 3. Arotational medical device as in claim 1, comprising two stationarycutting members on the tubular body.
 4. A rotational medical device asin claim 1, further comprising an annular recess in the tubular body forrotatably receiving the radially outwardly extending flange.
 5. Arotational medical device as in claim 1, wherein the rotatable tip has adiameter within the range of from about 0.025 inches to about 0.092inches.
 6. A rotational medical device as in claim 1, wherein therotatable tip has an axial length within the range of from about 0.040inches to about 0.120 inches.
 7. A rotational medical device as in claim1, wherein the distal end of the rotatable tip is approximately axiallyaligned with the distal end of the tubular body.
 8. A rotational medicaldevice as in claim 1, wherein the distal end of the rotatable tipextends beyond the distal end of the tubular body.
 9. A rotationalmedical device as in claim 1, wherein the rotatable tip is recessedwithin the tubular body.
 10. A rotational medical device as in claim 1,wherein the rotatable element comprises a torque tube.
 11. A rotationalmedical device as in claim 1, wherein the torque tube comprises a layerof braided wire.
 12. A rotational medical device as in claim 1,comprising a central guidewire lumen extending throughout the length ofthe rotational medical device.
 13. A rotational medical device as inclaim 3, wherein the rotatable tip further comprises a radially inwardlyextending annular recess.
 14. A method of removing material from avessel, comprising the steps of: providing an elongate, flexible,tubular body, having a proximal end and a distal end, a rotatable tip atthe distal end of the tubular body, and at least one stationary cuttingmember on the tubular body which cooperates with at least one flange onthe rotatable tip; advancing the distal end of the tubular bodytransluminally to the material; rotating the rotatable tip; and drawingportions of the material proximally past the rotatable tip so that thematerial is cut by the action of the flange rotating past the stationarymember.
 15. A method as in claim 14, wherein the drawing step isaccomplished by applying vacuum to the proximal end of the tubular body.16. A method as in claim 14, wherein the advancing step comprisesadvancing the tubular body along a guidewire.
 17. A method as in claim14, wherein the advancing step comprises advancing the tubular bodythrough a percutaneous access site.
 18. A method as in claim 14, furthercomprising the step of infusing fluid through a flush port on theproximal end of the tubular body.
 19. A method as in claim 14, whereinthe advancing step is accomplished by applying axial distal pressure onthe tubular body, and further comprising the step of reducing the amountof axial distal pressure in response to feedback indicating a change inthe load on the rotatable tip.
 20. A method as in claim 15, wherein theapplying a vacuum step is initiated prior to commencing rotation of therotatable tip.
 21. A method of removing material from a patient,comprising: providing an elongate flexible tubular body, having aproximal end, a distal end, and at least two radially inwardly extendingstationary cutting members near the distal end, a rotatable distal tipcarried by the distal end of the tubular body, the tip having at leasttwo radially outwardly extending flanges, and a control on the proximalend of the tubular body; advancing the distal tip of the tubular body tothe material to be removed; manipulating the control to activate avacuum through the tubular body; commencing rotation of the rotatabletip to remove material from the patient; and shearing the materialbetween the flanges and the stationary cutting members.